The present invention relates to organic light emitting devices (OLEDs), and more specifically to organic materials used in such devices.
Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.
As used herein, the term xe2x80x9corganicxe2x80x9d includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. xe2x80x9cSmall moleculexe2x80x9d refers to any organic material that is not a polymer, and xe2x80x9csmall moleculesxe2x80x9d may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the xe2x80x9csmall moleculexe2x80x9d class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be an fluorescent or phosphorescent small molecule emitter.
OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.
OLED devices are generally (but not always) intended to emit light through at least one of the electrodes, and one or more transparent electrodes may be useful in an organic opto-electronic devices. For example, a transparent electrode material, such as indium tin oxide (ITO), may be used as the bottom electrode. A transparent top electrode, such as disclosed in U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, may also be used. For a device intended to emit light only through the bottom electrode, the top electrode does not need to be transparent, and may be comprised of a thick and reflective metal layer having a high electrical conductivity. Similarly, for a device intended to emit light only through the top electrode, the bottom electrode may be opaque and/or reflective. Where an electrode does not need to be transparent, using a thicker layer may provide better conductivity, and using a reflective electrode may increase the amount of light emitted through the other electrode, by reflecting light back towards the transparent electrode. Fully transparent devices may also be fabricated, where both electrodes are transparent. Side emitting OLEDs may also be fabricated, and one or both electrodes may be opaque or reflective in such devices.
As used herein, xe2x80x9ctopxe2x80x9d means furthest away from the substrate, while xe2x80x9cbottomxe2x80x9d means closest to the substrate. For example, for a device having two electrodes, the bottom electrode is the electrode closest to the substrate, and is generally the first electrode fabricated. The bottom electrode has two surfaces, a bottom surface closest to the substrate, and a top surface further away from the substrate. Where a first layer is described as xe2x80x9cdisposed overxe2x80x9d a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is xe2x80x9cin physical contact withxe2x80x9d the second layer. For example, a cathode may be described as xe2x80x9cdisposed overxe2x80x9d an anode, even though there are various organic layers in between.
One application for phosphorescent emissive materials is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as xe2x80x9csaturatedxe2x80x9d colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art. CIE coordinates are described in H. Zollinger, xe2x80x9cColor Chemistryxe2x80x9d VCH Publishers, 1991 and H, J, A, Dartnall, J. K. Bowmaker, and J. D. Mollon, Proc. Roy. Soc. B (London), 1983, 220, 115-130, which are incorporated by reference.
Another application for phosphorescent emissive materials is a display, full color or otherwise, that is intended to be powered by battery, such as the display of a cellular telephone or a digital camera. For such applications, power efficiency is a particularly important parameter, because efficient emission may significantly extend battery life, and/or enable the use of smaller batteries. Lighting is another application where efficiency is of particular importance, because of the sheer volume of power used for lighting applications. Efficiency is also important for many other applications. Moreover, a high efficiency may lead to a longer lifetime, because inefficient devices generally lose power to heat instead of emitting light, and heat may adversely affect device lifetime.
An organic light emitting device is provided. The device includes an anode, a cathode, and an emissive layer disposed between the anode and the cathode. The emissive layer includes a material having the structure: 
M is a metal having an atomic weight greater than 40, m is at least 1, n is at least zero, Rxe2x80x3 is H or any substituent, X is an ancillary ligand, and A is selected from the group consisting of aryl and heteroaryl rings, and B is an aryl ring. A material including the photoactive ligand of the above material is also provided.